Move the class out of weld.hxx into its own header, in
order to make it easier to keep an overview and to avoid
having to recompile ~all UI code when the class is
modified.
Change-Id: If7cb4403f1861c465f44a1cae4065b0bf8dfad48
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/205323
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>